Method for quick quantitative analysis of the content of metallic aluminium in a bath of molten metals

ABSTRACT

THE ABOVE-MENTIONED METHOD WHICH COMPRISES DIPPING THE LOWER END PORTION OF A NONMELTABLE ELECTRODE ROD AS ONE SINGLE ELECTRODE IN A BATH OF MOLTEN METAL CONTAINING METALLIC ALUMINIUM; DIPPING IN SAID BATH AS THE OTHER SINGLE ELECTRODE THE LOWER END PORTION OF A STANDARD ELECTRODE DEVICE HAVING A SOLID ELECTROLYTE OF ALUMINUM USED AS AN OPERATING MEDIUM; DETERMINING AT THE KNOWN BATH TEMPERATURE THE POTENTIAL DIFERENCE BETWEEN BOTH SINGLE ELECTRODES CONSTITUTING A CONCENTRATION CELL HAVING ALUMINIUM IONS USED AS AN OPERATING MEDIUM; AND IMMEDIATELY FINDING THE PRECENTAGE CONTENT OF METALLIC ALUMINIUM IN SAID BATH BY REFERENCE TO A CALIBRATION GRAPH PREPARED BY OPERATING THE SAME TYPE OF CONCENTRATION CELL AS DESCRIBED ABOVE CONTAINING THE DIFFERENT KNOW CONCETRATIONS OF ALUMINUM UNDER THE SAME CONDITIONS EACH TIME.

Feb. 26, 1974 YOSHIHIKO KAWAI ETAL 3,194,569

METHOD FOR QUICK QUANTITATIVE ANALYSIS OF THE CONTENT OF METALLIC ALUMINIUM IN A BATH OF MOLTEN METALS Filed March 23, 1973 FIG FIG.2

POTENTIAL DIFFERENCE (mv) "United States Patent Ofi 3,794,569 Patented Feb. 26, 1974 3,794,569 METHOD FOR QUICK QUANTITATIVE ANALYSIS OF THE CONTENT OF METALLIC ALUMINIUM IN A BATH OF MOLTEN METALS Yoshihiko Kawai, Yokohama, and Mutsumi Ihida, Tokyo, Japan, assignors to Nippon-Kokan Kabushiki Kaisha, Tokyo, Japan Filed Mar. 23, 1973, Ser. No. 344,286 Claims priority, application Japan, Apr. 31, 1972, 47/ 32,473 Int. Cl. G01n 27/46 US. Cl. 204-1 T 5 Claims ABSTRACT OF THE DISCLOSURE The above-mentioned method which comprises dipping the lower end portion of a nonmeltable electrode rod as one single electrode in a bath of molten metal containing metallic aluminium; dipping in said bath as the other single electrode the lower end portion of a standard electrode device having a solid electrolyte of aluminium used as an operating medium; determining at the known bath temperature the potential difference between both single electrodes constituting a concentration cell having aluminium ions used as an operating medium; and immediately finding the percentage content of metallic aluminium in said bath by reference to a calibration graph prepared by operating the same type of concentration cell as described above containing the different known concentrations of aluminium under the same conditions each time.

This invention relates to a routine analysis for the manufacture of aluminium alloys accurately containing the prescribed amount of aluminium, which permits the quick determination of aluminium content in a bath of molten metals without sampling to control the addition of aluminium by reference to the results of said determination, thereby attaining the eflicient production of said alloys.

The prior art quantitative analysis for determining the content of aluminium in bath of molten metals has been carried out by the method which consists in crushing the solidified sample taken from the bath, dissolving the prescribed amount of said crushed sample in an acid solution and effecting the chemical analysis of said solution, or by the absorptiometric or atomic absorption method of determining the content of aluminium by measuring the absorbancy of said solution, or by the spectroanalytic method which comprises grinding the lumpy sample to the precribed shape and size, carrying out discharge with said sample used as one electrode and measuring the intensity of the aluminium spectrum appearing as the result of said discharge, thereby determining the aluminium content.

However, all those conventional analytic methods consist in first cooling molten samples taken from a bath for solifiication, crushing, cutting, grinding or dissolving said solidified samples as a preliminary step, and finally carrying out a complicated, time-consuming analytic procedure. Accordingly, one cycle of analysis requires a great deal of time and work. Moreover, said prior art analytic methods have the drawback that the content of nonmetallic aluminium, for example, aluminium oxide, contained by chance in the samples appears in an analytic results as if it constituted an integral part of metallic aluminium,

and consequently fail to be used in quick routine analysis required for accurate control of the aluminium content in manufacturing its alloys. Hitherto, therefore, efficient production of aluminium alloys having the prescribed quality has generally presented great difliculties.

This invention has been accomplished in view of the above-mentioned circumstances. An object of this invention is to provide a method for directly analyzing the con tent of aluminium from a bath consisting of its alloys without sampling.

Another object of this invention is to provide a method which, in the manufacture of aluminium alloys, permits the quick analysis of aluminium content in a bath of molten metals to control the addition of aluminium by reference to the results of said analysis, thereby attaining the efiicient production of high grade aluminium alloys accurately containing the prescribed amount of aluminium.

The above objects can be attained by the method of this invention which comprises dipping the lower end portion of a nonmeltable electrode as one single electrode in a bath of molten metal containing metallic aluminium; dipping in said bath as the other single electrode the lower end portion of a standard electrode device having a solid electrolyte of aluminium used as an operating medium; determining at the known bath temperature the potential difference between both single electrodes constituting a concentration cell having aluminium ions used as an operating medium; and immediately finding the percentage content of metallic aluminium in said bath of molten metal by reference to a calibration graph prepared by operating the same type of concentration cell as described above containing the different known concentrations of aluminium ions under the same conditions each time, said standard electrode device being constructed by using molten alumina or compounds mainly consisting thereof into a blind dense tube, placing molten pure metallic aluminium at the bottom of said tube and dipping the lower end of a nonmeltable electrode rod in said molten mass of aluminium.

Other important objects and advantageous features of this invention will be apparent from the following description and an accompanying drawing, wherein, for the present purpose of illustration only, specific embodiments of this invention at set forth in detail.

In the drawing:

FIG. 1 is a schematic longitudinal sectional view of a concentration cell used in the method of this invention;

FIG. 2 is a schematic longitudinal sectional view of a modification of said concentration cell used in the same as above; and

FIG. 3 is a calibration graph prepared by operating the concentration cell of FIG. 1 or 2 and measuring the potential difference between both single electrodes of said concentration cell derived from three kinds of molten aluminium alloy samples containing different known concentration of aluminium ions respectively.

There will now be described by reference to FIG. 1 the construction and function of the concentration cell used in the method of this invention. A bath 2 of molten aluminum alloy is held in a cell vessel 1. A nonmeltable electrode rod 3 has its lower end portion dipped in said bath as one single electrode. This rod 3 is made of molybdenum, tungsten, rhodium or platinum. On the other hand, a standard single electrode device 4 is prepared as follows. A dense blind tube 6, which is constructed by using a molten substance of alumina, spinel-type compounds such as MgO-Al O MnO-Al O FeO-Al O COO-A1 0 NiO-Al O and CuO-Al O or multi-type compounds such as Zn-Al O and 3Al O -2SiO has its bottom filled with molten mass 5 of pure aluminum or its alloy, for example, Cu-Al, Zn-Al or Fe-Al, containing a sufficient amount of aluminum to indicate a certain degree of its chemical potential. A nonmeltable electrode rod 7 is inserted into an insulating porcelain pipe 8, with the lower end portion of said electrode wire 7 dipped in the aforesaid mass 5 of molten aluminum or its alloy. The standard single electrode device 4 thus arranged has its lower end portion dipped in the previously described bath 2 of molten aluminum alloy. The concentration cell of.

FIG. 1 consists of the above-mentioned two single electrodes 3 and 4 with trivalent aluminum iOns used as an operating medium. A slug 9 floating on the surface of the bath 2 of molten aluminum alloy prevents the oxidation of said surface or a decline in the temperature of said bath 2. On the other hand, the mass of pure aluminum or its alloy has its surface hermetically sealed with cement mortar 10 so as to prevent the efflux of said mass 5 and securely fix the insulating porcelain pipe 8 in said Standard single electrode device 4.

A millivoltmeter 13 connected to the two electrode rods 3 and 7 through lead wires 11 and 12 measures the potential difference between said electrode rods 3 and 7. If, in this case, the standard free energy with which aluminum can be dissolved in a bath of molten metals at the temperature of said bath and the transport number of aluminum ions constituting a solid electrolyte are previously known, then it will be possible to determine the unknown content of metallic aluminum in said bath of molten metals from the potential differences measured with the millivoltmeter 13, using complicated electrochemical calculations. However, determination of the unknown content of aluminum directly from the measured electromotive force of the concentration cell instead of making such complicated calculations can be effected most quickly as well as most practically by previously providing the undermentioned calibration graphs, and carrying out said determination by reference thereto.

Namely, if the electromotive force of the same type of concentration cell as that of FIG. 1 is measured in advance with respect to a plurality of aluminum alloy samples whose aluminum contents are accurately known, and a calibration graph is previously prepared to indicate the interrelationship of the aluminum content with the potential difference between the two single electrode rods of said concentration cell, then it will be possible to determine immediately the aluminum content of unknown sample from the measured potential difference by reference to said calibration graph.

FIG. 2 illustrates a modified type of the standard electrode device. The concentration cell shown in FIG. 2 has the same arrangement as that of FIG. 1, excepting that electrode rod 7, insulating porcelain pipe 8 and hardened cement mortar 10 of FIG. 1 are replaced by a carbon rod 15 provided with a guard lid 14 at the top.

The method of this invention enables a routine analysis to be completed in less than 30 seconds, permitting the efficient production of aluminum alloys of constant quality.

This invention will be more fully understood by reference to the following example.

In a concentration cell constructed as shown in FIG. 1, a platinum electrode rod had its lower end portion dipped in a bath of Cu-Al alloy containing an unknown amount of aluminum, the temperature of said bath being 1100 C. There was also dipped in said bath a standard electrode device constructed by holding 50 g. of molten pure aluminum in a blind dense alumina tube and dipping the lower end portion of a platinum electrode wire in said molten pure aluminum, whose temperature was also 1100 C. At this condition, the electromotive force of the concentration cell was measured. The millivoltmeter attached to the cell indicated 350 mv. in about 10 seconds after the cell was started, and later maintained this voltage.

Prior to the above-mentioned determination of electromotive force, there had been provided a calibration graph. The cell was previously operated under the same condition each time to measure its electromotive forces corresponding to three kinds of molten Cu-Al alloy samples containing 0.02%, 0.5% and 1.0% by weight of aluminum respectively, the resultant electromotive forces indicating 510 mv., 205 mv. and m-v. respectively. Said electromotive forces plotted on a graph provided a calibration curve A shown in FIG. 3. Reference to the calibration curve A immediately determined the aluminum content corresponding to the afore-mentioned measured electromotive force of 350 mv. to be 0.09 weight percent.

What we claim is:

1. A method for quick quantitative analysis of the content of metallic aluminum in a bath of molten metals which comprises the steps of (a) providing a concentration cell containing a nonmeltable electrode rod and a standard electrode device, both of which have the lower end portions dipped in a bath of molten metals, said standard electrode device substantially consisting of a blind dense alumina tube, a molten mass of metallic aluminium received at the bottom of said alumina tube, and another nonmeltable electrode rod having its lower end portion dipped in said molten mass;

(b) measuring the potential difference between the two nonmeltable electrode rods in the step of (a); and

(c) determining the unknown content of aluminum in the bath of molten metals with reference to a calibration graph previously prepared from data on the different known aluminum concentrations in a plurality of samples by operating the same type of concentration cell as described above under the same conditions each time.

2. The method according to claim 1, wherein the nonmeltable electrode rods are made of a metal selected from the group consisting of molybdenum, tungsten, rhodium and platinum.

3. The method according to claim 1, wherein the nonmeltable electrode rod in the standard single electrode device is made of carbon.

4. The method according to claim 1, wherein the blind dense alumina tube is made of a spinel-type compound selected from the group consisting of A1 0 MgO-Al o MnO'Al2O FGO'Al O NiO'A1203, cuO'Ai203 and ZnO'A1203.

5. The method according to claim 1, wherein the blind dense alumina tube is made of 3Al O -2SiO References Cited UNITED STATES PATENTS 3,404,036 10/1968 Kummer et al 136-86 A 3,400,054 9/1968 Ruka et al 204-1 T 3,403,090 9/1968 Tajiri et a1 204- S 3,619,381 11/1971 'Fitterer 204-195 S FOREIGN PATENTS 1,189,365 4/1970 Great Britain 136-86 F OTHER REFERENCES Journal of Physical Chemistry, vol. 68, No. 9, September 1964, pp. 2444-9.

Trans. of the Metallurgical Soc. of AIME, vol. 236, January 1966, pp. 88-94.

TA-HSUNG TUNG, Primary Examiner US. Cl. X.R. 204-195 S 

